That's not the original tenon, but a Delrin replacement that was not properly attached.
An entire thread was devoted to the subject on the pipemakers forum:
Though it sounds reasonable and logical, there's no gunk holding it in place to dissolve, so if you haven't messed with dripping alcohol yet, don't bother.
In fact, before doing anything, check the hole in the face of the stem. Is it threaded? If yes, just screw the stem back on and remove the stuck tenon by twisting clockwise. Everything will be whole again---the tenon will be re-attached---and you're good to go as long as you remember to always twist to the right whether installing or removing the stem.
If the hole in the face of the stem is
not threaded, you can simply gently remove the tenon with some properly fitting pliers. (Doing that will likely leave some impressed grooves in the threads, but it's OK---some lengthwise grooves should have been put there to begin with).
Unless you have the tools to prepare the surfaces to re-glue the tenon, however, as well as the proper glue,
AND know how to avoid gluing the stem to the shank, removing it yourself will achieve nothing. You'll have to send the pipe to a repair guy.
PS --- the lack of pipe cleaner passage is part of the improper tenon install "package"... (Correctly done, that isn't a problem.)